Combinatorial chemistry holds the promise to significantly accelerate the pace of synthesizing hundreds and thousands of samples in different chemical composition, and the chemical properties of many samples and their reaction conditions are also measured and optimized simultaneously. At present, the success rate of combinatorial chemistry research in the field of catalysis mainly depends on the strength or weakness of overall reaction system design.
The development of combinatorial chemistry in the catalysis field is more challenging than in other fields, such as the superconductor, electromagnetics, and fluorescence material fields, mainly because: 1) the flow controller system of the reactor must ensure that the difference of the fluid flow rate in different channels is in an acceptable range (this problem does not exist in a batch reactor); 2) the reactor must be kept sealed under high temperature and pressure; 3) the temperature of catalysts in different reaction channels must be kept consistent.
Although the chamber-type reactor designed by Moates' group [Ind. Eng. Chem. Res. 1996, 35, 4801] achieved simultaneous reaction for a catalyst library, the testing data gathered by this reactor design didn't represent the real catalysts' properties. In this reactor design, the reactant drifted on the catalyst with poor flowing mode. Moreover, the reactant and product coexisted in the same chamber so they diffused into each other. Therefore, the results didn't reflect the real catalyst properties.
Jochen Lauterbach's group reported a catalytic combinatorial chemical reaction and detection system [J. Comb. Chem., 2000, 2, 243; Catalysis Today, 2001, 67, 357] in which they combined 16 fixed-bed reactors in parallel to form a combinatorial reactor. This publication didn't mention how the 16 channels of reactant gas were controlled.
The catalytic combinatorial reaction system designed by Senkan's group, which could test and evaluate the catalysts library, was actually a parallel reaction and detection system. Since this system didn't include a fluid distributor, the tiny back pressure difference in different catalyst channels would result in the differences of the fluid reactant flow. This produced a large relative error of the testing data and results.
Symyx Technologies Inc. developed a Catalysis Scanning Mass Spectroscopy (CSMS) system. In this system, a catalyst library was prepared on quartz glass, and a CO2 laser was used to heat individual catalysts in the library by heating specific locations on the back side of the quartz glass. An infrared (“IR”) temperature sensor was used to monitor the temperature of a specific catalyst. Concentric tubes were placed on the top of catalyst library and acted as reactant gas and product gas flow tube. The reactant gas passed through the inner tube and reacted with a catalyst surface and then passed out of the inner tube, and then the outer tube absorbed product gas and transferred the product gas to mass spectrometry for analysis. The process was accomplished in approximately 1 minute and only one catalyst was evaluated [Angew. Chem. 1999, 111, 508; Appl. 1998, WO-A98/15969]. This system was a traditional sequential analysis technology and couldn't be used for liquid reactions, so it didn't fulfill the requirement of high-throughput and parallel reaction mode. Moreover, heterogeneous catalysts generally need to be stabilized in the reaction environment for several hours before reaction takes place in order to produce reliable data on catalyst conversion and selectivity. Since a catalyst was only evaluated in a few minutes in this CSMS system, the data collected was not reliable. Also, the drifting flow mode on the quartz glass was very different from the fluid flow mode in a fixed-bed micro reactor.